Since a conventional socket has a fixed number and type of jacks, it is easy to cause a waste or a shortness of jacks due to different requirements for jacks and different numbers of electric appliances. For this, a socket device which can arbitrarily extend a number of jacks has been proposed, such as the socket device disclosed in Chinese Patent ZL201120198999.7, which realizes a plugging by providing a first socket having a plurality of jacks configured to plug with a second socket at one end side and a wire for connecting with the electric supply at the other end side and a second socket having a plurality of jacks at one side and a plug rod fitted with the plurality of jacks of the first socket at the other side. Thus, one first socket can be plugged with a plurality of second sockets sequentially.
However, in this conventional socket device, there is no security arrangement between the jack and the plug rod, and it is easy to cause accidents. Therefore, there is a need to improve and develop the conventional socket device.